advice on speaker matching, selection

New to the forum
Current set up:Custom built (Yaeger Audio) Freed-Williamson design tube amp rated at 25WRogue 66 preampRega 25 w/Grado Platinum 3Pioneer PD 65 through MSB Nelson Link III DACM&K S-1Bs speakers
I LOVE this amp.  It is so vintage sounding... very mellow, laid back, natural.  Obviously not a lot of power.  I live in a small apartment in a large high rise.  Therefore, I never play loud anymore.  My tastes run to jazz, classical, vocals.  I do still listen to rock (but less so).
The vintage MKs I'm running were well thought of in the day.  Unfortunately, I don't think their sensitivity is sufficient to be powered by 25W.  While the MKs are neutral and cast a wonderful sound stage, I'm not getting enough bass, nor inner detail/placement of the musicians in space.

As all of us know in this hobby, avoiding "going sideways" in the next purchase is paramount.
So... looking for opinions of stand mounted or SMALL floor standing speakers to enliven this rig and tastes.  Budget: $1-1.5K.  Thanks for your wisdom and experience in advance.  Peace